1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a capacitor having improved leakage current characteristics.
2. Description of the Related Art
As the degree of integration of semiconductor memory devices such as dynamic random access memory (DRAM) increases, methods of increasing the effective area of a capacitor, methods of reducing the thickness of a dielectric layer, and methods of increasing dielectric constant of the dielectric film are used to increase the amount of charge accumulated in a given cell area.
As is well known to those skill in the art, a capacitor includes first and second spaced-apart conductive electrodes with a dielectric layer therebetween. The first conductive electrode is often referred to as a storage electrode and the second conductive electrode is often referred to as a plate electrode. To increase the capacitance of a capacitor having a given physical size, the dielectric constant of the dielectric layer can be increased. Many materials have been investigated for their high dielectric constant. For example, tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and titanium dioxide (TiO2) have been widely used, but they exhibited problems such as unacceptably large leakage current in thin films, when material having high dielectric constant is used for the capacitor, a polysilicon layer and a titanium nitride (TiN) layer are generally used for the first conductive electrode and the second conductive electrode of the capacitor, respectively. However, the interfaces between the first conductive electrode and the dielectric layer and between the dielectric layer and the second conductive electrode are unstable. When the interfaces are unstable, leakage current characteristics are distorted, rendering the semiconductor device unstable.
To reduce unstable characteristics between the first conductive electrode and the dielectric layer, a silicon nitride (SiN) layer formed therebetween may be used. The SiN layer may be formed on the polysilicon layer by a rapid thermal nitridation (RTN) process, the polysilicon layer being formed as the first conductive electrode. And then, the dielectric layer is formed on the SiN layer to reduce unstable characteristics. But, in case of using tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and titanium dioxide (TiO2) as a dielectric layer, the RTN process may not be used between the dielectric layer and second conductive electrode such as TiN because of absence of silicon in the dielectric layer.
Accordingly, a need exists for a method of manufacturing a capacitor having improved leakage current characteristics.
A method for manufacturing a capacitor of a semiconductor device is provided, which includes the steps of: forming a first electrode on a semiconductor substrate; forming a dielectric layer on the first electrode; forming a second electrode on the dielectric layer; first annealing the capacitor having the first electrode, the dielectric layer, and the second electrode under oxygen atmosphere; and second annealing the capacitor having the first electrode, the dielectric layer, and the second electrode under vacuum.
According to an aspect of the present invention, the method further includes the step of forming a buffer layer on the first electrode. The buffer layer is formed by rapid thermal nitridation (RTN) with a plasma of gases including one of nitrogen and oxygen. The gases including nitrogen includes a gas selected from the group consisting of NH3, N2O, and N2. The gases including oxygen includes a gas selected from the group consisting of N2O, O2, and a gas from a hydroxyl group. The buffer layer includes a layer formed from a material selected from the group consisting of Si3N4 and SiON.
According to a preferred embodiment of the present invention, the first electrode includes a layer formed from a material selected from the group consisting of polysilcon, tantalum (Ta), titanium (Ti), platinum (Pt), molybdenum (Mo), tantalum (Ta) nitride, titanium (Ti) nitride, and molybdenum (Mo) nitride. The first electrode includes impurity doped polysilicon.
According to a preferred embodiment of the present invention, the dielectric layer includes a layer formed from a material selected from the group consisting of silicon nitride, silicon oxide, tantalum oxide (Ta2O5), aluminum oxide (Al2O3), and titanium oxide (TiO2). The second electrode includes a layer formed from a material selected from the group consisting of polysilicon, tantalum (Ta), titanium (Ti), platinum (Pt), molybdenum (Mo), tantalum (Ta) nitride, titanium (Ti) nitride, and molybdenum (Mo) nitride.
According to a preferred embodiment of the present invention, the step of the first annealing is performed using oxygen containing gas at a temperature of about 200xc2x0 C. to about 500xc2x0 C. The oxygen containing gas includes a gas selected from the group consisting of O2 gas, N2O gas, O3 gas, and mixtures thereof. The oxygen containing gas comprises oxygen of about 0.01% to about 100%. The step of the second annealing is performed at a temperature of about 300xc2x0 C. to about 700xc2x0 C.